Current limiting circuit breaker with collapsible cradle structure



April 7, 1970 C I AQSTROBEL 3,505,622 CURRENT LIMITING CIRCUIT BREAKERWITH COLLAPSIBLE CRADLE STRUCTURE Fileauomzl, 1968 6Sheets-$heet1 IN VENTOR 6 7 fifffi d N M U Aprxl 7, 1970 A. .STROBEL CURRENT LIMITINGCIRCUIT BREAKER WITH COLLAPSIBLE CRADLE STRUCTURE Filed Nov. 21, 1968 Ie Sheets-She et z A ril 1, 1970 COLLAPSIBLE CRADLE STRUCTURE sSheets-Sheet 5 Filed NOV. 21, 1968 M m V NJ 1 m 1 I ML 3 Lu m mlmm April7, 1970 I A. STROBEL I I 3,505,622

CURRENT LIMITING CIRCUIT BREAKER WI'II-I COLLAPSIBLE CRADLE STRUCTUREFiled Nov. 21, 1968 6 Sheets-Sheet 4 April 7, 1970 AQSTROBEL 3,505,622

CURRENT LIMITING- CIRCUIT BREAKER WITH COLLAPSIBLE CRADLE STRUCTUREFiled Nov. 21, 1968 e Sheets-Sheet 5 April 7, 1970 AUSTROBEL 3,

CURRENT LIMITING CIRCUIT BREAKER WITH COLLAPSIBLE CRADLE STRUCTURE FiledNov. 21, 1968 s Sheets-Sheet e \xJ k INVENTOR. 445aerszeaaz4 UnitedStates Patent 3,505,622 CURRENT LIMITING CIRCUIT BREAKER WITHCOLLAPSIBLE CRADLE STRUCTURE Albert Strobel, Cherry Hill, N.J., assignorto I-T-E Impenal Corporation, Philadelphia, Pa., a corporation ofDelaware Filed Nov. 21, 1968, Ser. No. 777,821 Int. Cl. H01h 77/02 US.Cl. 335-16 5 Claims ABSTRACT OF THE DISCLOSURE In a circuit breakerdevice whereupon the contact blowoff forces accompanying a severe faultcondition serve to collapse a two-part cradle structure, a toggle typecradle biasing arrangement is disclosed. The two portions of the cradlestructure are normally maintained as a rigid integral member by a springbiased toggle linkage structure. The use of the toggle linkage forbiasing the collapsible cradle permits a reduction in the biasing springrequirements, and hence an attendant reduction in the overall circuitbreaker size.

My invention relates to current limiting circuit breakers of the typeshown and more fully discussed in my copending US. patent applicationSer. No. 777,704 filed on even date herewith and assigned to the sameassignee of the present application. That patent application shows acurrent limiting circuit breaker device which upon the occurrence of asevere fault condition of a predetermined magnitude, utilizes theblowoff forces generated at the main contact pair to defeat the latchmeans of the main circuit breaker mechanism. The release of the latchmeans under such conditions is obtained by the provision of acollapsible portion of the operating mechanism latch train; That is, thelatch train includes at least one member having a pair of relativelymovable portions. These relatively movable portions are biased into acertain fixed relationship by a biasing means of a calibratedpredetermined retention force. Under normal operation of the circuitbreaker, as for example in the contact engaged, manual off, and thetripping of the circuit breaker upon operation of the conventionalthermal or magnetic trip device, these two operative portions functionas a single integral rigid member. Their integral relationship ismaintained by the force of a latch retention biasing means. Upon theoccurrence of a severe fault condition, the contact blowoif forcesgenerated at the contact pair are transmitted to the collapsibleportions of the latch in opposition to the latch retention biasingmeans. The collapse of these latch portions then serves to release themain operating mechanism latch.

As discussed in my aforementioned pending US. patent application Ser.No. 777,704, it is advisable that for most rapid operation of thecircuit breaker, the collapsible portion of the latch train should beclosest to the contacts, and hence the cradle is usually used.Accordingly, the principal disclosed embodiment of that applicationshows a two-part spring loaded collapsible cradle mechanism. The biasingof the cradle in the previous embodiments is obtained by means of acompression or tension spring directly connected to the relativelymovable portion of thelcollapsible cradle. These springs on the cradleare required in addition to the biasing springs of the overcenter toggleutilized in the circuit breaker main operating mechanism. The loadrequirements of the auxiliary cradle spring is dependent upon the forceof the main circuit breaker operating mechanism spring as well as thecontact pressure maintained on the circuit breaker .contacts. Atincreasing load ratings of the circuit breaker,

these forces tend to correspondingly increase, thereby requiring moresubstantial spring forces for use in conjunction with the collapsiblecradle. I have, therefore, experienced that in the larger frame size ofmolded case circuit breakers constructed in accordance with myinvention, a substantial space may be required to physically locate thebiasing spring means provided in conjunction with the collapsible cradlemechanism. This in turn increases the size of the circuit breakermechanism and hence the overall size of the breaker.

The present invention is directed to an improved means of biasing thecollapsible cradle in conjunction with a toggle mechanism, therebyutilizing the mechanical advantage of the toggle mechanism to reduce therequired spring size. Basically, the manner in which the togglemechanism operates in conjunction with its associated biasing meanspermits the use of a substantially lower biasing force than previouslyrequired in the structures of aforementioned US. patent application Ser.No. 777,- 704. The biasing meansis illustratively shown as a spring,whose principal purpose is to hold the toggle mechanism of the cradleagainst a stop. In the illustrative embodiment a torsion spring isshown, located about the toggle knee. However, this is done forillustrative purposes only, with it being understood that anappropriately located tension or compression spring may also beutilized, with such tension or compression spring being of significantlylesser force (and hence size) than the springs necessitated by theprevious embodiments. The toggle knee is operatively connected to themovable contact, as by a hook-like member intermediate the contactcarrier arm and the toggle knee. In the event of contact arm movementcaused by blowoff, the hook-like lever moves the toggle knee overcenterwith respect to its biasing spring, thereby collapsing this latchretention toggle mechanism. The collapse of the latch retention togglemechanism is accompanied by the collapse of the cradle. This results inthe movement of the cradle portions to effect release of the operatingmechanism latch, and hence movement of the main circuit breakerovercenter toggle mechanism to the contact disengaged condition.

It is, therefore, a principal object of the present invention to providean improved biasing arrangement in conjunction with a collapsible cradlestructure of a current limiting circuit breaker.

A further object of the present invention is to provide, in conjunctionwith a current limiting circuit breaker having a collapsible cradle, animproved retention arrangement for the collapsible cradle, whichcomprises an overcenter toggle means.

Another object of my present invention is to provide a spring biasingarrangement in conjunction with a collapsible cradle, which utilizes themechanical advantage of a toggle structure to reduce the requisitespring forces.

These as well as other objects of my invention will become apparent upona consideration of the following description and drawings in which:

FIG. 1 shows a current limiting circuit breaker, constructed inaccordance with my invention, in the contact engaged condition.

FIGS. 2 and 3 sequentially show the operation of the circuit breaker ofFIG. 1 upon the occurrence of a moderate overload or fault condition,causing operation of the conventional type of overload trip unitmechanism.

FIG. 4 shows initial movement of the circuit breaker mechanism upon theoccurrence of a severe short circuit condition, with the contacts beingseparated by blowoff forces to obtaincurrent limiting action and thecradle being collapsed thereby releasing the operating mechanism latch.

FIGS. 5 and 6 sequentially follow FIG. 4, and show release of thecircuit breaker operating mechanism by the auxiliary latch, and ultimateoperation of the main circuit breaker toggle.

Referring to the figures, circuit breaker is of the same general typediscussed in conjunction with my aforementioned US. patent applicationNo. 777,704 and includes a molded housing having a main body portion 12and cover 14. The circuit breaker includes at least one pair of contactsfor each phase, having a stationary contact 22 connected to lineterminal 24. The cooperating movable contact 26 is mounted on a contactarm 28, which in turn is pivotally mounted at 30 to contact carrier 32.Contact pressure forces for urging the cooperating contact pair 22, 26in good intimate electrical engagement are obtained by the spring forceof the contact operating mechanism 50 and the contact pressure means 34.The contact carrier 32 is pivotally mounted to an operating mechanismframe (not shown) at pivot 36. The circuit breaker 10 may typically be amulti-phase device, with the various phases interconnected by tie bar38, for coordinated multi-phase operation, in the well known manner.

The movable contact arm 28 is electrically connected to the trip unitassembly by means of an appropriate conductor means, generallysimplified by the braid 40. In actual practice, the trip unit assembly20 which is typically an integral and replaceable assembly is connectedto the contact arm 28 by separate contact carrier straps, which arebolted together during the insertion of the trip unit assembly. Tripunit assembly 20 includes a magnetically actuated fault conditionedresponsive means 41 including a stationary magnet 42 and cooperatingarmature 44. The trip unit assembly 20 may also include the wellknowntype of thermally responsive bimetal element (not shown), responsive toa sustained moderate overload condition. Upon the occurrence of apredetermined overload fault condition, the armature 44 moves toward thepole face of magnet 42 as shown in FIG. 2, thereby moving the armaturestem 46 downward and rotating the tripper bar 48 counterclockwise. Thisserves to defeat the latching engagement between the tripper bar 48 andlatch member 45.

The circuit breaker operating mechanism 50 includes an overcenter togglemeans having a lower toggle link 52, upper toggle link 54 and springbiasing means 56. Spring biasing means 56 is connected at its lower endsto the toggle knee 68, and at its upper end to the manual operatinghandle 15. A latchable cradle is provided which comprises two relativelymovable portions 58 and 60, pivoted about upper toggle bearing 62.

In accordance with the present invention, the relatively movableportions 58, 60 of the cradle are maintained in the position shown inFIG. 1 by a latch retention means, including toggle linkages 80 and 82.One end of toggle linkage 80 is pivotally mounted to the cradle portion58 at 81. The opposed end of toggle linkage 82 is similarly pivotallymounted to the cradle portion 60 at 83. The

toggle links are connected together at the toggle knee 84 which alsoserves to mount the torsion type biasing spring 86. The auxiliary togglelinkage 80, 82 therefore serves to move the cradle portion 58, 60 apartabout their pivot 62, as limited by the stop 61. As long as the toggle80, 82 is maintained as shown in FIG. 1, it will serve as a retentionarrangement to maintain the cradle portions 58, 60 as a single rigidmember.

The means for moving the toggle linkages 80, 82 overcenter andcollapsing the cradle is provided by the hookshaped lever 90, which isconnected at one end 91 to the contact arm 28. The opposite end of thelever includes the hook-shaped portion 92, which operatively engagesextension lever 94, mounted to the toggle link 82.

The operation of the circuit'breaker will now be discussed:

Reference is now made to FIG. 2, which illustrates the condition uponthe occurrence of a moderate overload or fault current condition abovethe normal load carrying 4 capacity of the circuit breaker but withinits conventional trip rating. The magnetic fault responsive operatingmeans 41 of the trip unit 20 has been actuated, thereby rotating thetripper bar 48 counterclockwise and releasing the tip 51 of the latchlever 45. This, in turn, serves to permit rotation of auxiliary latch 66releasing latch tip 65 of the cradle portion 58. The cradle assembly(comprising portion 58, 60, toggles 80, 82 and their biasing spring 86),now rotates as a single integral rigid member about pivot 83.Referringnow to FIG. 3, the main mechanism toggle linkage 52, 54 has nowmoved overcenter with respect to the main operating spring 56, at whichpoint the rigid cradle assembly has completed its movement to the cradlestop 67 and the contacts have completely parted. It should be noted thatthe latch train comprising elements 48, and 56 have now returned totheir Original positions (as shown in FIG. 1) under the influence ofappropriate biasing means, and the tripping cycle has been completed.Following the sequence from FIGS. 1-3, it should again be recognizedthat the two-part cradle 58, and its associated toggle mechanism 80, 82has moved as an integral member following the actuation of the trip unitassembly 20. Similarly, the cradle portions 58, 60 will be maintained asan integral member should the circuit breaker be moved to the manual OFFposition (not shown).

Reference is now made to FIGS. 4-6, which sequentially indicate theoperation of the circuit breaker when subjected to a severe faultcondition, substantially in excess of that discussed in conjunction withthe operation of FIGS. 2 and 3. The magnitude of the severe faultcondition causes a rapid initial contact blowoff as shown in FIG. 4,resulting in the pivoting of contact arm 28 about its pivot 30. This inturn causes downward movement of hook type lever 90 mounted to the rearof the contact arm. The hook end 92 engages toggle linkage lever 94,thereby moving the cradle biasing linkage 80, 82 overcenter with respectto the condition shown in FIG. 1. Mechanical forces pushing upward atthe cradle pivot 62 serve to pull the latched portion 94 outward fromunderneath the hook tip 92. This in turn causes relative movement of thecradle portions 58, 60, such that the cradle tip is released fromlatching portion 63 of the auxiliary latch 66. The cradle, once freed,continues to rotate clockwise about pivot 83 to the condition shown inFIG. 5. As shown therein, the toggle linkages 80, 82 of the cradleassembly are still held below their locked-in center by the hook lever92. Referring sequentially to FIG. 6, the cradle has completed itsmovement to the cradle stop 67 and the contacts are fully opened, withthe main toggle mechanism 52, 54 having been moved to overcenter withrespect to its spring 56. The extension lever at the auxiliary toggleknee 94 has ben released from the hook 92, thereby permitting the cradletoggle 82 to move back into the locked-in position under the influenceof biasing spring 86. The tripping cycle is now completed, and it shouldbe recognized that the condition of the circuit breaker of FIG. 6corresponds to that shown in FIG. 3.

Although there has been described a preferred embodiment of this novelinvention, many variations and modifications will now be apparent tothose skilled in the art. Therefore, this invention is to be limited,not by the specific disclosure herein, but only :by the appendingclaims.

The embodiments of the invention in which an exclusive privilege orproperty is claimed are defined as follows:

1; In a circuit breaker comprising at least one cooperating pair ofstationary and movable contacts;

an operating mechanism connected to said movable contact for moving saidmovable contact between an engaged and disengaged condition relative tosaid stationary contact; said operating mechanism including a latchablecradle and first biasing means tending to move said cradle towards acontact disengaged condition; said cradle including a latchable tipnormally in latched engagement with a latching member during contactengagement;

said latchable tip, when disengaged from said latching member, allowingmovement of said cradle under the influence of said first biasing meansto the contact disengaged condition;

a first fault responsive operating means responsive to overload currentsof a first predetermined nature for automatically moving said latchingmember out of latched engagement with said cradle tip for defeating saidlatched engagement. and permitting movement of the cradle to the contactdisengaged condition;

a second fault responsive operating means responsive only to faultcurrents of a second predetermined nature substantially in excess ofsaid first predetermined nature, for automatically moving said latchabletip out of latched engagement with said latchable member and permittingmovement of the cradle to the disengaged conditions;

said second fault responsive operating means constructed to respond toits operative fault current condition and defeat said latched engagementin a substantially more rapid manner than required for the operation ofsaid first fault responsive means;

said cradle having first and second relatively movable operativeelements, one of which includes said latchable tip;

a latch retention means urging said operative elements to a firstposition whereby said-cradle operatively functions as a single integralmember under conditions of contact engagement and the movement of saidcontacts other than by said second fault responsive means;

said latch retention means including a second biasing 0 means;

said second biasing means urging said operative cradle elements towardssaid first position;

said second fault responsive operating means generating a latch releaseforce in opposition to said second biasing means for causing said oneoperative cradle element to move relative to 'the other element into arelease position, serving to move said latchable cradle tip out oflatched engagement with said latching member;

said second fault responsive operating means utilizing the blowoifforces at the contact pair to provide said latch release force;

said contact pair being urged together in the engaged condition by apredetermined contact pressure force;

said predetermined contact pressure force operatively related to aspecific magnitude of the blowoff forces accompanying fault currentmagnitudes of said second predetermined nature, such that the blowoffforces will be insuflicient to overcome said contact pressure force andsecond biasing means until the fault current magnitude reaches saidsecond predetermined nature;

the improvement comprising:

said latch retention means including an overcenter toggle meansincluding first and second toggle links;

each of said links having opposed first and second ends;

the first end of said first toggle link connected to said first cradleoperative element;

the first end of said second toggle link connected to said second cradleoperative element;

the second ends of said toggle links connected together to form a toggleknee;

force directing means directing said latch release force to said toggleknee to move said toggle means overcenter with respect to said secondbiasing means;

said overcenter movement of said toggle knee moving said one operativecradle element from said first position to said release position,thereby serving to release the latched engagement of said latchablecradle tip.

2. In a circuit breaker, as set forth in claim 1:

said second biasing means being a spring means operating about saidtoggle knee.

3. In a circuit breaker, as set forth in claim 1:

said force directing means including a direct linkage member betweensaid movable contact and said toggle knee;

said direct linkage member moving responsive to the blowoff inducedmovement of said movable contact to directly translate said toggle kneeovercenter.

4. In a circuit breaker, as set forth in claim 1:

said movable contact carried by a pivotally mounted contact arm;

said force directing means including a direct linkage member betweensaid movable contact arm and said toggle knee;

said direct linkage member moving responsive to the blowofi inducedmovement of said movable contact arm to directly translate said toggleknee overcenter. 5. In a circuit breaker, as set forth in claim 2: saidspring means being a torsion spring positioned about said toggle knee.

References Cited UNITED STATES PATENTS 3,251,232 5/1966 Harper 3351743,384,845 5/1968 Johnson 33516 3,384,846 5/1968 Heft 335-16 BERNARD A.GILHEANY, Primary Examiner H. BROOME, Assistant Examiner US. Cl. X.R.

